IMPROVED RUBBER MODIFIED POLYSTYRENE

Abstract: High impact polystyrene resins are provided having a surprisingly good combination of toughness and gloss characteristics. Such resins contain small (i.e. 0.1 to 0.4 micron) capsule morphology rubber particles in combination with relatively small (i.e. 0,25 to 1 micron) entanglement morphology rubber particles. It has been found that such resins are capable of providing izod impact strength values in the range of 2.5 to 3.5 ft-lb/in (133.4 to 186.7 J/m) and higher at an overall volume average rubber size of less than 0.4 micron with corresponding gloss values in excess of 90 percent.

Description: IMPROVED RUBBER MODIFIED POLYSTYRENE The present invention pertains generally to impact resistant styrenic resin compositions and to processes for the preparation thereof More particularly, sucn invention specifically relates to rubber-modified styrenic polymers in wnich the dispersed gra ted rubbery polymer particles exhibit at least two distinctly different ruober particle morphologies and satisfy certain critical size and content reαuirements for each of the respective types of rubber particles Rubber modified polystyrene resins constitute a generally known category of materials which finα practical utility in a wiαe variety of injection molding and extrusion applications. In recent times, substantial attention has been directed to improving the overall performance properties and characteristics of such resin materials by modifying and controlling the average size, the size distribution and the morphology of the grafted rubber particles that are dispersed throughout the continuous polystyrene matrix phase of such resin compositions For example, in Dupre's U.S. Patent 4, 146,589 (issued March 27, 1979), there is disclosed a continuous mass polymerization process for preparing a bimodal particle sized high impact polystyrene (HIPS) composition in which a first diene rubber/styrene monomer solution is partially polymerized to form 0.5 to 1 micron-sized dispersed rubber particles; a second diene rubber/styrene monomer solution is partially polymerized to form 2 to 3 micron-sized dispersed rubber particles; and the two resulting partially polymerized mixtures are then combined and further polymerized to the desired final degree of styrene monomer to polymer conversion According to this particular reference, a good gloss/toughness balance occurs with the resulting resins when the 0.5 to 1 micron particles constitute from 70 to 95 percent of the rubber particles and the remaining 5 to 30 percent is composed of the 2 to 3 micron particles Echte et al.'s U.S. Patent 4,493,922 (issued January 15, 1985) is also concerned with bimodal rubber particle-sized HIPS compositions. In particular, the compositions of concern therein are predominantly (i.e., 60 to 95 weight percent on a butadiene weight basis) composed of 0.2 to 0.6 micron rubber particles having a so-called "capsule" morphology (also variously referred to in the art as "single occlusion" or "core/shell" morphology) in combination with from 5 to 40 weight percent (on a butadiene only weight basis) of 2 to 8 micron particles having a cellular or "coil" particle morphology. Kasahara et al.'s U.S. Patent 5,039,714 is quite similar to the above-discussed Echte et al. patent insofar as it is premised upon a bimodal HIPS composition containing a relatively small (i.e., 0.1 to 0.6 micron) particle size αispersed rubber component having a single occlusion (or "capsule") morpnology and a relatively larger dispersed rubber component having a cellular morphology which Kasahara et al. also refersto as a "salami" morphology. Kasahara et al. does differ from Echte et al. in that the volume averaged particle size of its cellular particle component is required to be from 0 7 to 1.9 micron. -1- SUBSTfTUTE SHEET (RULE 26) Other Known types of dispersed rupber oarticie morpnology which can oe ootameα under the proper graft polymerization conditions in the preparation of rubber modified polystyrene resins include the so-called entanglement (or "labyrinth") morpnology (i.e., wherein polystyrene inclusions within the ruober oarticie appear as irregularly curved, elongated domains of polystyrene separated by relatively thinner elongated layers of rubber) and the so-called concentric shell or "onion skin" morpnology which is characterized by alternating generally spheπcai or elliptical polystyrene layers and rubber layers HIPS resins having these latter types of rubber particle morphology are αescπbed in some detail in published European Application Number 0048390 (March 31 , 1982) and are taught as being particularly effective for use in blends with polyphenylene ether resins. According to this reference, the overall average particle size of the dispersed rubber particles should be in the range of from 0.5 to 3 micron. More recently (i.e., in published European Application Number 0460541 of December 11 , 1991), entanglement rubber particle morphology has been taught as being an equivalent alternative to cellular rubber particle morpnology in the context of certain tπmoda! particle-sized HIPS compositions. In accordance with this latter reference, an improved property balance as between gioss and impact strength is provided by HIPS compositions which contain from 40 to 98 weight percent of 100 to 600 nm (0.1 to 0.6 micron) capsule morphology rubber particles in combination with from 2 to 60 weight percent of a mixture of cellular and/or entanglement morphology rubber particles, from 1 to 60 weight percent of which have a size of from 200 to 1 ,200 nm (0.2 to 1.2 micron) and 40 to 99 weight percent of which have a size of from 1 ,200 to 8,000 nm (1.2 to 8 micron). In connection with the foregoing, it has heretofore been generally accepted, conventional wisdom that it was essential in order to obtain good toughness (e.g., Izod impact strength) properties in mass, solution or mass/suspension polymerized high impact polystyrene (HIPS) resin compositions that there be present therein at least some minimum portion of a dispersed rubber particle population in the size range from 1 to 2 microns or greater. Surprisingly, however, it has now been discovered that HIPS resin materials containing dispersed rubber particles having entanglement (or "labyrinth") or concentric shell (or "onion skin") morphology exhibit very good Izod impact strength characteristics at overall volume average rubber particle sizes of less than 1 micron (and even at overall volume average sizes of less than 0.5 or 0.6 micron) and even under circumstances (i.e., particle size distributions) wherein there are essentially no rubber particles present having a size of one micron or larger. One very key significance or benefit of this discovery resides in what it means from a practical standpoint in terms of the gloss/impact strength balance which can be achieved with the HIPS resins in question. Thus, for example, the entanglement morDhology- Dased HIPS resins hereof are caoaole of providing, at a outadiene ruober content of 8.5 - 9 -2- SUBSTITUTE SHEET (RULE 2ζ) weight percent (on a poiybutadiene weight basis), an 80 + percent 60° Gardner gioss value (injection molded test specimen) in comoination with a 2 ft lb/in (106.7 J/m) Izoα impact strength as determined using a compression molded test specimen. In contrast, a comparaole (i.e., 8.5 weight percent poiybutadiene-containing) conventional monomodal cellular particle- based HIPS resin will typically provide an Izod impact strength of only 1 ft lb/in (53.35 J/m) or less at the average particle size that is required (i.e., 0.5 micron) to obtain an 80 percent gloss value. Another noteworthy feature of the subject entanglement morphology-based resins is that they are capable of being produced on conventional, commercial scale continuous mass or solution polymerization trains at rubber contents (again on a poiybutadiene weight basis) up ■ Q to 15 weight percent or more. When so produced, such resins are capable, at the relatively small particle sizes which are hereinafter more fully discussed, of providing 90 + (injection molded) percent gloss values in combination with Izod impact strengths (compression molded) of 4.5 ft lb/in (240 J/m) or more. In light of the foregoing, the present invention can be viewed as being in one of ■ 5 its aspects an improved rubber-modified monovinylidene aromatic polymer composition which has a very distinctive and highly advantageous combination of impact strength and gloss characteristics. Generally speaking, said composition comprises, on a total composition weight basis, from 90 to 55 weight percent of a rigid monovinylidene aromatic polymer matrix and, dispersed within said matrix, from 10 to 45 weight percent of grafted and occluded 1 ,3- 20 alkadiene-based rubber particles, said particles being composed, on a rubber particle weight basis, of: a. from 25 to 80 weight percent of rubber particles having a capsule morphology and a volume average particle size of from 0.1 to 0.4 micron; and b. from 75 to 20 weight percent of rubber particles having an entanglement 25 morphology and having a volume average particle size of from 0.25 to 1 micron. In another of its aspects, the present invention also takes the form of a method for preparing the above-described entanglement rubber particle morphology-based rubber- modified polymer compositions. In this latter regard, such invention is characterized as being a method for the preparation of the above-described rubber-modified monovinylidene aromatic 0 polymer composition, said method comprising: a. dissolving from 5 to 30 parts by weight of a 1 ,3-alkadiene/monovιnyiidene aromatic block copolymer rubber in from 95 to 70 parts by weight of a monovinylidene aromatic monomer, said block copolymer rubber being one which has from 15 to 40 weight percent of monovinyiidene aromatic monomer 35 copolymerized therein; b. polymerizing the resulting rubber/monomer solution at a temperature of from 50 to 210 °C, in the presence of from 0 to 1000 parts Der million by weight of a polymerization initiator and from 0 to 2000 parts per million by weignt of a chain transfer agent ano under agitation conditions sufficient to provide capsule morpnology ano entanglement moronoiogy ruober particles in the aoove- specified size ranges; and c. thereafter recovering the resulting rubber-modified monovinylidene aromatic polymer product. As used herein throughout the remainder of this document, the terminology "entanglement morphology" shall be used to geneπcally mean or connote the various known non-ceilular HIPS rubber particle morpnologies tnat are commonly referred to in the art as "entanglement", "labyrinth", "coil ", "onion skin" or "concentric circle" morphology. Similarly, the term "capsule" morpnology shall be used throughout the remai nder hereof to geπerically connote those known very small rubber particles that have a morphology which is commonly also referred to in the art as "single occlusion" or "core/shell" morphology. Detailed Description of the invention The rubber-modified monovinylidene aromatic polymers nereof contain a predominant amount (e.g., 55-90 percent) by weight of a rigid continuous matrix phase which is composed, in polymerized form, of one or more monovinylidene aromatic monomers and, dispersed within said continuous matrix phase, a minor amount (e.g., 10 to 45 percent) by weight of discrete rubbery polymer particles that are composed of an elastomeπc polymer material or "substrate" having portions of monovinylidene aromatic polymer chemically grafted thereto and physically occluded therein and that satisfy the particle size and morphological criterion which are set forth above. Monovinylidene aromatic monomers suitable for use herein include those corresponding to the formula X CH 2 = C I Ar wherein X is hydrogen or an alkyl radical containing from 1 to 3 carbon atoms and wherein Ar is phenyl, alkylphenyl, halophenyl or alkylhaloDhenyl. Examples of such monomers thus include styrene, alpha-methylstyrene, alpha-ethylstyrene, vinyl toluene, aipha- methylvinyltoluene, o- and p-ethylstyrene, 2,4-dimethylstyrene, o-bromostyrene, p- chlorostyrene, 2,4-dichlorostyrene and the like. Styrene itself is especially preferred on the basis of its cost and ready availability. Eiastomeπc polymer materials which are suitable for use in the preparation of these rubber-modified polymer compositions include rubbery 1 ,3-alkaPiene polymers having a second oroer transition temperature of 0°C or less (preferably -20°C or less) and thus -4- SUBSTITUTE SHEET (RULE ?6) include 1 ,3-alkadιene nomoDOiymers ano coooiymers containing, in DOiymeπzeα form ana on a eiastomeric polymer weignt basis, from 60 to 100 percent of a 1 ,3-alkaoιene monomer (e.g., butadiene, isoprene, etc.) ano from 0 to 40 weignt percent of one or more monoethylenically unsaturated comonomers sucn as styrene, acryionitπle. aloha-methylstyrene, methacrylonitπie, methyl methacryiate, ethyl acrylate, etc. Particularly preferred eiastomeric polymer suostrates for use herein are 1 ,3-alka- diene/monovinylidene aromatic (e.g., 1 ,3-buta-diene/styrene) block coDoiymer rubbers which contain from 60 to 85 weight percent of the 1 ,3-alkaoιene monomer biocκ copoiymeπzed with from 15 to 40 weight percent of one or more monovinylidene aromatic monomers. Such materials are especially preferred by virtue of the relative ease by which they can be caused to have the desired capsule and entanglement particle morphologies in commercial scale bulk or solution graft polymerization processes and equipment and at commercially feasible initiator and chain transfer agent usage levels. The indicated rubber-modified monovinylidene aromatic polymers are conveniently prepared by dissolving from 5 to 30 parts by weight of the aforementioned eiastomeric polymer material in from 95 to 70 parts by weight of the monovinylidene aromatic monomer and polymerizing the resulting elastomer/monomer solution at an elevated temperature in the presence of from 0 to 1000 parts per million (by weight) of a polymerization initiator and from 0 to 2000 parts per million (by weight) of a chain transfer agent and under agitation conditions sufficient to provide two different types of grafted/occluded rubber particles one of which has capsule morphology and the other of which has entanglement morphology and which have volume average particle sizes falling, respectively, within the above specified individual size ranges. If desired, the polymerization reaction mixture can also contain from 1 to 30 (preferably from 5 to 20) weight percent (on a total reaαion mixture weight basis) of an inert solvent or diluent such as ethylbenzene, etc. The indicated polymerization process will typically be conducted at a temperature of from 50to 210°C and is preferably conducted at a temperature in the range of from 90 to 190 (more preferably 105 to 185)°C. Suitable polymerization initiators for use herein include any of the known oii- soluble initiators which decompose to form free radicals such as the various known peroxide initiators such as benzoyi peroxide, dicumyl peroxide, di-tert-butyl peroxide, etc.; azo compounds such as azobutyronitnle and the like. As noted above, such initiators are typically employed in an amount ranging from 0 to 1000 parts per million (ppm). Preferably, they are used in amounts ranging from 0 to 500 (more preferably 0 to 200) ppm. Chain transfer agents suitable for use herein include those which are already well known to be useful in the preparation of styrenic polymers. Exemplary of such known chain transfer agents are organic thiois and dithiols such as butyl mercaptan, n- or t-doαecyl mercaptan, lauryl mercaptan, stearyi mercaptan, Denzvi mercaDtan, cycloheximercaptan, 1 ,6- nexanedithiol, etc.; halogenated hydrocaroons sucn as caroon tetrachlonde, carbon tetrabromide, bromotπcnioromethane ana the like. Typically, said chain transfer agents are used in an amount ranging from Oto 2000 ppm ana, preferably in amounts ranging from 0 to 1500 (especially O to 1000) ppm. While the level of the chain transfer agent and the initiator cnosen for use herein can individually be zero for either one of them, it should be noted that one or the other of them will typically be used in some minimum non-zero amount. In connection with the foregoing, it can also be noted that combined initiator and chain transfer agent usage levels play a key role in controlling the rubber particle size and morphology within the rubber-modified styrenic resins obtained from the subject graft polymerization process. Within such process, the use of increased initiator levels generally tend to increase the level of grafting on the rubber particle and makes it easier to obtain the desired entanglement and capsule rubber morphologies wnen using styrene/butadiene block copolymer rubbers containing relatively low styrene content. Increased usage levels of chain transfer agent generally tend to result in larger overall average grafted rubber particle size within the resulting HIPS resins. Also, within such process, it can be noted that the particle sizing mechanism appears to be predominantly a chemical sizing phenomenon in which agitation rate at the point of phase inversion plays only a minor role in determining and/or controlling the size of the resulting grafted rubber particles. The amount of chain transfer agent and polymerization initiator used also serves to control the molecular weight of the monovinylidene aromatic polymer (e.g., polystyrene) formed during the indicated graft polymerization process. Typically, the free (i.e., ungrafted) monovinylidene aromatic polymer matrix formed during said polymerization will have a weight averaged molecular weight (Mw) of from 130,000 to 250,000 (preferably from 150,000 to 220,000); a number averaged molecular weight (Mn) from 40,000 to 100,000 (preferably from 45,000 to 75,000); and Mw:Mn ratio of from 2 to 5 (preferably from 2.2 to 3.5). One further, and rather surprising, feature of the subject rubber-modified monovinylidene aromatic polymer compositions is that they exhibit notably good toughness characteristics (e.g., Izod impact strength values) even at relatively low matrix phase molecular weights (e.g., in the range of Mw = 130,000 to 150,000 and Mn = 35,000 to 50,000) at which conventional cellular rubber morphology-based HIPS resins tend to exhibit little or no toughness. The total rubber content of the rubber modified monovinylidene aromatic polymer compositions hereof, stated on a 1 ,3-alkadiene weight basis only, is typically from 5 to 30 (preferably from 8 or 10 to 20 or 25) weignt percent on a total rubber modified polymer composition weight basis. -6- SUBSTITUTE SHEtT (RULE 26) The dispersed, grafted and occiudeα ruDOer particles themselves will typicaily have, per one part by weight of the starting point ungrafted ruober, from 0.5 to 4 or 5 (preferaoiy from 1 or 1.5 to 3 or 4) parts by weignt of monovinylidene aromatic polymer grafted thereto ana occluded therein. Accordingly, the total or combined weight of the grafted and occluded rubber particles (i.e., including polymerized, grafted and occluded monovinylidene aromatic polymer portions thereof) wiil typically constitute from 10 to 45 (preferably 15 or 20 to 35, 40 or 45) weight percent of the overall rubber modified polymer composition with the remainder thereof (i.e., 55 to 90, preferably from 55, 60 or 65 to 75 or 80, weight percent) being free (i.e., non-grafted and non-occluded) matrix material. The indicated total weight of the grafted and occluded rubber particles (i.e., including the weight fraction thereof attributable to grafted and occluded monovinylidene aromatic polymer) will correspond generally to the parameter which is commonly referred to as "gei content" and which is typically determined experimentally by dissolving a known quantity of the rubber-modified resin of interest (or more specifically that portion of it which will dissolve) in a suitable solvent for the monovinylidene aromatic polymer matrix resin (typically toluene); separating the undissolved portion thereof from the polymer/solvent solvent solution; drying the undissolved residue and determining the weight thereof. The "gel content" thus determined (as a fraction or percentage of the initial dry sample weight) corresponds to the combined content of the insoluble, crossiinked rubber constituent and that portion of the grafted and occluded monovinylidene aromatic polymer material that is chemically grafted thereto, or sufficiently physically entrapped therein, so as to remain with the insoluble rubber material. As has been noted above, the dispersed grafted and occluded rubber particles of the subject polymer compositions wiil be present in at least two distinct particle morphologies, namely one group of particles having a so-called capsule (or single occlusion) morphology and a volume averaged size in the range of from 0.1 to 0.4 micron and a second group having an entanglement (or onion skin) morphology and having a volume averaged particle size in the range of from 0.25 to 1 micron. Typically, the individual particles making up the first group (i.e., the capsule morphology population) will individually range in size from as little as 0.05 micron to as much as 1 micron with the overall volume averaged size taken over all members of said group being in the 0.1 to 0.4 micron range noted above. Preferably, the volume average size of the indicated capsule morphology group or population will be from 0.2 to 0.35 micron. Generally speaking, the capsule morphology rubber particles will as a group constitute from 25 to 80 weight percent of the grafted/occluded rubber particles contained within the subject compositions. More preferably, however, said capsule morphology particles will constitute a minor portion (e.g., from 25 to 45 or 50, especially from 25 to 40, weight -7- SUBSTΪTUTE-SHEET (RULE 26) oercent) of the comoineo weight of all of tne grafted ano occiuαed rubber particies contained therein. The entanglement (or onion sxin) morphology rubber particles hereof typically range, in terms of their individual particle size, from 0.2 to 3 micron in diameter and, as a group, generally have a voiume averaged size in the range of from 0.25 to 1 micron. Preferably such entanglement particles have a volume average size in the range of from 0.3 or 0.35 to 0.8 microns. It is also generally preferred that the entanglement particle group or population be substantially free (e.g., contain, on an entanglement particle weight basis, less than 10 percent, preferably less than 5 percent and most preferably less than 0.5 percent) of particles having a o particle diameter in excess of 1 micron. While the indicated entanglement morphology rubber particles can generally constitute anywhere from 20 to 75 percent of the total weight of grafted/occluded rubber particles contained within the subject resin composition, it is generally preferred that such entanglement particles constitute a predominant portion (e.g., from 50 or 55 to 75, especially 5 from 60 to 75 weight percent) of the combined weight of the entanglement and capsule morphology particles contained therein. Another preferred criterion associated with an especially preferred subcategory of the subject polymer compositions is that the overall volume averaged particle size (i.e., taken over both of the above-described capsule and entanglement morphology particles) be less than 0 0.6 micron, most preferably 0.5 micron or less and especially less than 0.5 micron. Satisfaction of this particular criterion facilitates the obtention of extremely good gloss properties while still obtaining excellent impact strength characteristics. In one especially preferred embodiment hereof, the above-described dual rubber particle-based (i.e., combined capsule morphology/entanglement morphology) resin 5 composition further comprises a relatively minor amount (e.g., from 1 to 25, preferably from 2 to 15, weight percent on a total grafted/occluded rubber particle weight basis) of conventional cellular morphology grafted/occluded 1 ,3-alkadiene-based rubber particles. Typically, the indicated cellular morphology rubber particles that are optionally employed herein wiil be characterized as having an overall size distribution ranging from 0.3 0 (preferably 0.6) micron at its small end up to 5 (preferably 4) micron at the large end and will have an overall voiume average particle size (i.e., taken only over those particles having a cellular morphology) of from 0.6 to 1.2 (preferably from 0.8 to 1.0) micron. The above described ternary (i.e., capsuie + entanglement + cellular) morphology embodiment can be employed, if desired, in the context of the full range of binary 5 capsule/entanglement morphology-based compositions that are discussed above. However, such embodiment is most beneficially employed in the context of those combined capsule/entanglement morphology compositions hereof in wnich the capsule morphology particies have a volume average diameter toward the low end of their generally applicable size -8- siBsrmJT SHEET (RULE 26) range (i e , tnus oeing in the 0 1 to 0 2 or 0 25 micron average size range) ana especially wnen said relatively smail-sizeα capsule moronoiogy particles constitute a predominant proportion (e g., from 50 to 80 weignt percent) of the comomeo weignt of the grafted/occluoed entanglement and capsule morphology particles The further inclusion of the inαicated cellular moronoiogy rubber particles is also generally beneficial and preferred in those instances wnerein the entanglement rubber particles have a volume average particle size within the lower reaches of its generally a p plicable average size range (i e , thus being in the 0 25 to 0 35 or 0 4 micron average size range). In preparing the above-αescnbed ternary capsule/entangiement/cellular rubber morphology-based resin compositions, the inαicated cellular morpnology grafted/cccluded rubber particle constituent can, if desired, be introαuced thereto by simply extrusion compounding the above-described binary capsuie/entanglement morphology-based compositions hereof with the desired amount (on a grafted/occluded rubber particle weight basis) of a separately prepared conventional 1 ,3-alkaαιene homopolymer or copolymer rubber- modified styrenic resin having a monomodal particle size distribution and a cellular rubber particle morphology and having the desired volume average rubber particle size within the above-specified size range. On the other hand, the indicated cellular morphology rubber particle constituent can also be prepared in-situ as part of a single overall graft copolymeπzation process. In such case a minor amount (e.g., 2 to 20 weight percent) of a solution of 1 ,3-alkadιene (especially 1 ,3- butadiene) homopolymer or copolymer rubber in the monovinylidene aromatic monomer can simply be fed, in non-polymerized or partially graft polymerized (phase inverted or not) form, into the above-described binary capsule/entanglement morphology-based resin graft polymerization process at a point therein following, and preferably only shortly after, phase inversion of the main polymerization mixture and thereafter completing the polymerization process under agitation conditions sufficient to cause the cellular morphology particles resulting from the post-inversion addition of the rubber/monomer feed stream solution to be in the desired average size range. Rubbery 1 ,3-alkadιene polymers suitable for use in the in-situ formation of the cellular morphology grafted/occluded rubber polymer particies include those having a second order transition temperature of 0 β C or less (especially -20°C or less) and include 1 ,3-alkadιeπe homopolymers and copolymers containing from 60 to 100 weignt percent of a 1 ,3-alkadιene monomer (especially 1 ,3-butadιene) and from 0 to 40 weight percent of one or more monoethylenically unsaturated monomers such as styrene, acrylonitnle, methacryionitπle, methyl methacrylate, etc. Typically, the post-phase inversion monomer/rubbery polymer feed stream solution employed forthe in-siτu formation of the cellular rubber particle will have a rubbery -9- SUBSTITUT- SHEET (RULE 26) oolymer content in the range of from 5 to 30 (especially from 8 or 10 to 20 or 25) weignt oercent on a oost -phase inversion feed stream weight basis and will be added to the main oinary capsule/entanglement resin polymerization process at a point therein wnen the main feed stream has achieved a monovinylidene aromatic monomer-to-polymer conversion of from 5 ' 0 to 60 (especially from 25 to 45) percent. The actual determination of the rubber oarticie morphology ana particle size characteristics of the subject polymer compositions is readily accomplished using conventional Transmission Electron Micrograph (TEM) techniαues on thin slices of the polymer material in question and known osmium tetraoxide staining techniques. 1 o When so-analyzed and characterized (typically at a magnification in the range of from 9,000 to 30,000 times), the above specified separate particle morphologies will be readily observed and recognized in the resulting photomicrographs. These same photomicrographs can then also be used to ascertain (a) the outermost size range limits for the individual members of the different types of rubber particles, (b) the volume averaged sizes of the 15 different morphology groups taken separately, and (c) the overall volume average size of all rubber particles taken collectively. In determining the different volume averaged sizes noted above, the following formula is applied to the photomicrograph image for the particular group or population of particles which is of interest: 20 D - ΣNiD.4 ΣNiDi3 wherein Dv = the voiume averaged diameter; and Ni = the number of particles having the specific morphology of interest and having a diameter __ in given size, Di. The polymer compositions hereof are fully usable with the full spectrum of conventional additives (e.g., pigments, dyes, plasticizers, lubricants, stabilizers, mold release agents, etc.) that have long been used with previous types of HIPS compositions. Moreover, these new compositions are suitable for use in a wide variety of practical injection molding and 30 extrusion applications including those wherein conventional HIPS resins have been used historically as well as in many more demanding applications in which more expensive resins (e.g., ABS, etc.) have heretofore been required. The present invention is further illustrated and understood by reference to the following examples thereof in which all parts and percentages are on a weight basis unless 3 _ otherwise specifically indicated. Within such examples, the various properties that are measured are determined as follows: Melt Flow Rate ASTM D- 1238-86 at 200 °C and 5.0 Kg. -10- SUBST1TUTE SHEET (RULE 26) Izod Impact Strength ASTM D-256-84 using compression molded test specimens Tensile Properties ASTM D-638-87b Gloss 60° Gardner gloss taken on injection moiαed test specimens. General Procedures for the Working Examples: A series of HIPS resins having a combined caDSuie/entangiement rubber morphology were maαe in a three stirred tube reactor polymerization system connected in a series arrangement. A styrene/butadiene block copolymer rubber was used and was dissolved in styrene and then pumoed to the reaαor system. Ethyl benzene, a diluent, was added prior to the entry into the reactors. Initiator and cnain transfer agent were added to control the amount of polystyrene grafting to the rubber and the molecular weight of the grafted material. The initiator and chain transfer agent also control the molecular weight of the ungrafted polystyrene matrix resin. The initiator was either added direαly to the feed or was pumped into a transfer line running between the rubber dissolver and the initial reaαor of the reaαor system. The chain transfer agent was either added with the initiator or in the early stages of the first reaαor. The combination of initiator and chain transfer agent serves as the dominant faαor in controlling the rubber morphology and the rubber particle sizes. Agitation of the polymerizing mass during phase inversion has less significant influence on the rubber morphology and the rubber particle size than the indicated initiator and chain transfer effeαs. Afterthe partially polymerized reaαion mixture undergoes phase inversion (typically at a conversion of from 15 to 60 percent of styrene monomer to polymer) and the rubber morphology and rubber particle size were set, the polystyrene matrix molecular weight can be controlled by the addition of additional chain transfer agent. This was usually done when the polymerizing mixture was between 50 and 60% solids. The styrene polymerization was continued in the second and third reaαors until the solids were approximately 75 - 85% . The temperature profile of the entire reaαor system increased from 1 10°C at the beginning to approximately 180°C atthe end. The temperature range of the first reaαor was approximately 110 β Cto 138°C, the second reaαor ranged from 138°C to 145°C, and the third reaαor ranged from 145° to 180°C. The polymerized mass then was direαed enters a devolatilization unit to remove the diluent and residual styrene and to crosslink the rubber. Example 1 A sample of HIPS was made having a 14.6 weight percent butadiene content using 21 weight percent of a 70/30 butadiene/styrene block copolymer rubber, 3.25 weight percent mineral oil, and with the balance being styrene. The resin was made with a linear three stirred tube reaαor system. Each reaαor had three temperature control zones. The main feed stream composition was 6.3 weight percent ethyl benzene, 2.5 weight percent mineral oil, 16.5 weight percent 70/30 block copolymer, and with the balance being styrene monomer. A n- dodecyl mercaptan, n-DDM, feed stream consisting of 98.4 weight percent ethyl benzene and 1.6 weight percent n-DDM was added to the first zone of the first stirreα tube. The feed rate of tne main feed was 0.75 Ib/hr (340.2 g/hr) ana the n-DDM feea rate was 0.034 Ib/hr ( 15.42 g/hr) The temperature running from zone numoer one to zone number nine was 1 13. 127, 135, 138, MO, 142, 144, 146 and 150°C, respectively. The properties of the resulting HIPS resin are set forth in Table I below. Example 2 A sample of HIPS was made having 13.4 weight percent butadiene content using 19.1 weight percent of a 70/30 butadiene/styrene block copolymer, 2.8 weight percent mineral oil, and with the balance being styrene. The resin was maαe using a linear stirrer tube reaαor system. Each reactor consists of three temperature zones. The main feed stream composition was 7.5weιght percent ethyl benzene, 2.4 weight percent mi nerai oil, 15.6 weight percent block copolymer, and with the balance being styrene monomer. The main feed rate was 8614 g/hr. A feed stream consisting of 1 weight percent 1 ,1-di(t-butylperoxy)cyclohexane, 1 weight percent mineral oil with the balance of ethyl benzene was added to the first zone at the rate of 43 g/hr. A feed stream consisting of 11.1 weight percent oαadecyl 3,5-di-tert-butyl-4- hydroxyhydrocinnamate, 3.2 weight percent n-dodecyi mercaptan, with the balance of ethyl benzene was added to the first zone at a rate of 94 g/hr. A feed stream consisting of ethyl benzene was added to the eighth zone at a rate of 451 g/hr. The temperatures for zones 1 through 9were 1 15, 120, 124, 127, 135, 142, 148, 156 and 165°C respectively. The reaαioπ mixture was devolatilized in two stages, first at 184 C C and 850 mm Hg and the second at 246°C and 21 mm Hg. The properties of the resulting resin material are found in Table I below. Examples 3-8 Several additional HIPS resin samples were prepared using the equipment and procedures set forth in Examples 1 and 2 above. The particle size and distribution and the relative proportion of capsule morphology particles and entanglement morphology particles was vaπeα among these examples by varying the amount of initiator [1 ,1 di-(t-butylperoxy) cyclohexane) and chain transfer agent (n-dodecyl mercaptan) employed therein. The properties of the resulting resin samples are summarized in Table I below. -12- SUBSTrTUTE SHEET (RULE 26) TABLE I Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Example 7 Example 8 Composition PBD (wt. percent) 14.6 13.4 13.4 14.6 8.5 13.5 14.6 14.6 SBR (wt. percent) 21 19.1 19.1 21 12.1 19.3 21 21 Mineral Oil (wt. percent) 3.25 2.8 2 9 3.25 3.0 2.9 3.25 3.25 CO ez Properties oo 2. Ty (m Pa) 19.6 19.0 19.2 20.5 22.5 21.6 24.4 17.8 Tr (m Pa) 15.2 15.0 15.4 16.0 17.4 16.7 18.8 13.4 Tm x 103 (m Pa) 1.38 1.43 1.43 1.46 1.89 1.61 1.81 1.25 Elongation (percent) 12 21 14 13 26 17 25 17 Izod (J/m) 246.5 128.0 176.1 149.9 69.4 37.3 28.8 131.8 P 3 Melt Flow Rate (g/10 min) 4.27 3.1 3.0 3.30 3.1 2.9 2.00 8.74 Vic_t ("C) 99 4 101.2 101.6 99 9 102 5 101 6 100 8 98 2 TABLE I CONTINUED Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Example 7 Example 8 Mw 170100 181 100 183400 174100 203500 193300 222500 137200 Mn 68770 70420 68770 70420 85090 81720 81720 43690 Mz 313000 318100 313000 318100 354000 417000 417000 279300 Gloss 84 93 N.D.* N D.* 99 97 N D * N D.* Capsule Sizei (micron) 0.27 0.26 0.25 0.26 0.23 0.20 0.18 0.36 O CZ wt. % of Capsule 37.9 33.2 33.5 44.7 68.3 53.9 77.9 27.3 CO Particles Entanglement Size 2 (micron) 0.64 0.46 0.43 0.41 0.41 0.29 0.27 1.02 CΛ m rx. _ wt. % of Entanglement 62.1 66.8 66.5 55.3 31.7 46.1 22.1 72.7 -Α I Particles <__ • CZ Overall Vol .Ave. Particle Size (micron) S3 0.57 0.42 0.40 0.36 0.34 0.25 0.21 0.95 Initiator** (ppm) 0 50 50 0 200 100 200 0 Chain Transfer 700 350 350 200 200 400 450 1900 Agent*** (ppm) * N.D. = Not Determined ** 1,1 Di (t-butylperoxy) cyclohexane *** n- dodecyl mercaptan 1. Volume average size of capsule morphology particles. 2. Volume average size of entanglement morphology particles. 3. Volume average size of all rubber particles in the Composition. As can be seen from the results in Tabie I, the best Izoα impact strength appears to be obtained in the Example 1 resin at an overall voiume average particle size of 0.6 micron. As can also be seen, however, excellent imoact strength properties are aiso ootained in examples 2 and 3 at an overall volume average particle size of 0.4 to 0.5 microns while giving notably higher gioss vaiues. By way of comparison, it has been observed that conventional monomodal particle size distribution cellular rubber morpnoiogy-based HIPS resins, at a butadiene content of 8.5 weight percent, must typically have a volume average particle size of 2.5 to 3 microns in order to attain an Izod impaα strength of 133.4 J/m (2.5 ft-lb/in). Such conventional resins typically exhibit a 60 degree Gardner gloss value of less than 50 percent at the indicated 2.5 to 3 micron average rubber particle size value. Conversely, it has also been observed that conventional cellular rubber particle morphology-based HIPS resins having a monomodal particle size distribution can (at the indicated 8.5 weight percent butadiene content) be caused to attain gloss values in the 80 to 90 range by decreasing the volume average particle size thereof to 0.5 micron. However, in that small rubber particle size range, the resulting conventional HIPS resins typically exhibit an Izod impaα strength of only 53.35 J/m (1 ft-lb/in) or less. Example 9 A sample of HIPS was made having a 10.5 weight percent butadiene content using 15 weight percent of a 70/30 butadiene/styrene block copolymer rubber, 3.25 weight percent mineral oil, and with the balance being styrene. The resin was made with a linear three stirred tube reaαor system. Each reaαor had three temperature control zones. The main feed stream composition was 8.7 weight percent ethyl benzene, 2.5 weight percent mineral oil, 1 1.9 weight percent 70/30 block copolymer, 100 ppm 1 , 1-di(t-butyl peroxy) cyclohexane and with the balance being styrene monomer. A n-dodecyl mercaptan, n-DDM, feed stream consisting of 99.77 weight percent ethyl benzene and 0.23 weight percent n-DDM was added to the first zone of the first stirred tube. The feed rate of the main feed was 0.75 Ib/hr (340.2 g/hr) and the n-DDM feed rate was 0.034 Ib/hr (15.42 g/hr). The temperature running from zone number one to zone number ni ne was 110, 117, 128, 138, 142, 144, 147, 150 and 155°C, respeαiveiy. The properties of the resulting HIPS resin are set forth in Table II below. Example 10 Example 9 was substantially repeated with the exception that a second rubber/styrene monomer feed stream solution was added to zone number 5 of the nine zone, 3 reaαor system (i.e., at a point in the polymerization process at which 43 percent of the styrene monomer originally present in the main feed stream had been converted to styrene polymer). The second feed stream had the same compositional make-up as the main feed stream and was fed to the polymerization process at a rate of 50 g/hr. -15- SUBSTITUT SHEET (RULE 26) The resulting HIPS resin was one wnich containeα three αifferent ruDDer oarticie morpnologies (i.e., capsule, entanglement ana cellular) and had the DroDerties ana characteristics as summarized in Table II below. While the present invention nas been αescri bed and illustrated with reference to particular embodiments and examples thereof, such is not to oe interpreted as in any way limiting the scope of the instantly claimed invention. -16- SUSSTITUTE SHEET (RULE 26) TABLE II Example 9 Example 10 Composition PBD (et. percent) 10.5 10.5 SBR (wt. percent) 15 15 Mineral Oil (wt. percent 3.25 3.25 Properties Ty (m Pa) 23.1 21.9 Tr (m Pa) 17.7 15.5 Tm x 103 (m Pa) 2.09 2.07 Elongation (percent) 9 23 Izod (J/m) 25.8 90.2 Melt Flow Rate (g/10 min) 4.6 4.3 Vicat fQ 100.9 102.2 Mw 192600 189100 Mn 54400 65000 Mz 376800 362600 Gloss ' 100 96 Capsule Size (micron) 1 about 0.2 about 0.2 wt. % of Capsule Particles about 55 about 48 Entanglement Size (micron)* about 0.3 about 0.3 wt. % of Entanglement about 45 about 39 Particles Cellular Size (micron) 4 None about 0.9 wt. % of Cellular Particles None 13 Overall Vol. Ave. Particle Size (micron)3 about 0.25 about 0.33 Initiator (ppm)** 100 100 Chain Transfer Agent*** 100 100 Footnotes 1-3, ** and *** - See Table I above. 4. Volume average size of cellular rubber particies.

Claims: WHAT IS CLAIMED IS: 1. A method for the preparation of a rubber-modified monovinylidene aromatic polymer composition said composition comprising, on a total composition weight basis, from 90 to 55 weight percent of a rigid monovinylidene aromatic polymer matrix and from 10 to 45 weight percent of grafted and occluded 1 ,3-alkadiene-based rubber particles dispersed within said matrix and wherein from 25 to 80 weight percent of said rubber particles have a capsule particle morphology and a volume average particle size of from 0.1 to 0.4 micron and from 75 to 20 weight percent of said particles have an entanglement particle morphology and a volume average particle size of from 0.25 to 1 micron; said method comprising: a. dissolving from 5 to 30 parts by weight of a 1 ,3-alkadiene/monovinylidene aromatic block copolymer rubber in from 95 to 70 parts by weight of a monovinylidene aromatic monomer, said block copolymer rubber being one which has from 15 to 40 weight percent of monovinylidene aromatic monomer copolymerized therein; b. polymerizing the resulting rubber/monomer solution at a temperature of from 50 to 210°C, in the presence of from O to 1000 parts per million by weight of a polymerization initiator and from 0 to 2000 parts per million by weight of a chain transfer agent and under agitation conditions sufficient to provide capsule morphology and entanglement morphology rubber particles in the above- specified size ranges; and c. thereafter recovering the resulting rubber-modified monovinylidene aromatic polymer produα. 2. The method of Claim 1 wherein the monovinylidene aromatic monomer is styrene. 3. The method of Claim 2 wherein the block copolymer rubber is a block copolymer of 1 ,3-butadiene and styrene. 4. The method of Claim 3 wherein the 1 ,3-butadiene/styrene block copolymer has from 20 to 30 weight percent of styrene copolymerized therein. 5. The method of Claim 1 wherein the polymerization initiator is seleαed from the group consisting of alkyl peroxides. 6. The method of Claim 1 wherein the chain transfer agent is seleαed from the group consisting of alkyl mercaptans. 7. The method of Claim 1 wherein from 2 to 15 parts by weight of a solution containing from 5 to 30 weight percent of a 1 ,3-alkadiene homopolymer or copolymer rubber dissolved in a monovinylidene aromatic monomer is added to the polymerization process as a separately added second feed stream at a point in the process subsequent to that at which the initial monomer/rubber solution nas onase inverted to from tne αisDβrseα grafteα aπα occiuded rubber particles having capsule ana entanglement ruober particie morαhoiogy. 8. A rubber-modified monovinylidene aromatic poiymer composition wnich comprises, on a total composition weight basis, from 90 to 55 weight percent of a rigid monovinylidene aromatic polymer matrix and, dispersed within said matrix, from 10 to 45 weight percent of grafted and occluded 1 ,3-alkadiene-oased rubber particles, said particles being composed, on a rubber particle weight basis, of: a. from 25 to 80 weight percent of rubber particles having a caosuie morphology and a volume average particie size of from 0.1 to 0.4 micron; and b. from 75 to 20 weight percent of rubber particles having an entanglement morphology and having a volume average particle size of from 0.25 to 1 micron. 9. The poiymer composition of Claim 8 wherein the matrix polymer has a weight averaged (Mw) molecular weight within the range of from 130,000 to 250,000, a number average molecular weight (Mn) of from 40,000 to 100,000 and Mw: Mn ratio of from 2 to 5. 10. The polymer composition of Claim 8 wherein the matrix polymer constitutes from 70 to 55 weight percent of said composition and wherein the grafted and occluded rubber particles constitute from 30 to 45 weight percent thereof. 11. The polymer composition of Claim 8 wherein the rubber content of said composition on an 1 ,3-alkadiene only weight basis is from 8.5 to 20 weight percent of the total composition. 12. The polymer composition of Claim 8 wherein the capsule morphology rubber particles constitute from 25 to 50 weight percent of the total grafted and occluded rubber particies and wherein the entanglement rubber particles constitute from 50 to 75 weight percent thereof. 13. The polymer composition of Claim 12 wherein the capsule morphology particles have a volume average particles size of from 0.2 to 0.35 micron and wherein the entanglement morphology particles have a voiume average particle size of from 0.35 to 0.8 micron. 14. The polymer composition of Claim 8 wherein said composition has a compression molded Izod impaα strength of at least 213.4 J/m and a 60° Gardner gloss of at least 80 percent. 15. The polymer composition of Claim 8 wherein said composition exhibits a 60° Gardner gloss value of at least 90 percent and a compression molded an Izod impaα strength of at least 133.4 J/m. 16. The polymer composition of Claim 8 which further contains, on a total composition weight basis, from 1 to 5 weight percent of mineral oil. 17. The poiymer composition of Claim 8 which further contains, on a total grafted/occluded rubber particle weight basis, from 2 to 15 weight percent of dispersed grafteα ana occluded 1 ,3-alkadιene-σasea homoooiymer or coooiymer ruooer oarticies navmg a cellular rubber Darticle morphology and having a volume average Dartide size of from 0.6 to 1.2 micron. -20- SIBSTITUTE SHEET (RULE 26)

Inventors: HEIRES MARK D, SCHRADER DAVID, SODERQUIST MARK E, HEIRES, MARK, D., SCHRADER, DAVID, SODERQUIST, MARK, E.
Applicants: DOW CHEMICAL CO, THE DOW CHEMICAL COMPANY
Application year: 1994
Main classification: C08L287
IPC codes: C08F2, C08F285, C08F287, C08L25, C08L51